JP2000294928A - Via hole forming method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To relax aspect ratio and to easily form a uniform via hole. SOLUTION: In this via hole forming method, a first mask 508 having a large hole 521a is placed on a photosensitive insulating material 507, and a first exposure operation is performed by a first light 510 having a first light intensity. A first developing operation is performed, and a large hole 521b is formed on the photosensitive insulating material 507. A second mask 509 having a small hole 522a is placed on the large hole 521b on the photosensitive insulating material 507, and a second exposure operation is performed by a second light 511 having a second light intensity. A second developing operation is performed, and a small hole 522b is formed between the large hole 521b on the photosensitive insulating material 507 and a land 506, and thereby, a via hole 520 is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method of forming a via hole, and more particularly to a method of forming a via hole in a multilayer printed wiring board.

[0002]

2. Description of the Related Art FIGS. 2A and 2B are process sectional views showing a first conventional example. To form a via hole in a printed wiring board by a build-up method, a lower wiring 2 is formed on a substrate 1 by etching or the like, and a photosensitive resin 3 that can be an insulating layer is applied and dried to form a via hole. Exposure is performed by masking the portion. Thereafter, by developing, as shown in FIG.
Is formed.

Here, an overhang portion 3a is formed above the via hole 4. Therefore, in order to remove the overhang portion 3a, after the resin is completely cured, buffing is performed, and the resin is roughened using permanganate or the like, and as shown in FIG. Then, the photolithography process of the plating resist and the electroless copper plating 5 and the electrolytic copper plating 6 (upper wiring) are performed, so that the upper wiring 6 and the lower wiring 2 are connected. In forming a multilayer, these steps are repeatedly performed.

However, in the method described above, after the via hole is formed, overhang occurs due to the photosensitive characteristics of the resin, and if the subsequent wet process is performed as it is,
Bubbles in the via holes are not sufficiently discharged due to overhangs, so that the treatment solution is poorly circulated around the via holes and may be defective in the plating step. Also, when performing buffing or the like to remove the overhang,
Since the applied insulating layer is lost more than the thickness of the overhang, it is necessary to apply a thicker layer in advance, and the overhang portion breaks into the via hole during buffing, so that the overhang cannot be reliably removed. And so on.

FIGS. 3A and 3H are process sectional views showing a second conventional example (for example, Japanese Patent Application Laid-Open No. 08-064968).
Reference). (1) As shown in FIG. 3A, a glass epoxy substrate 11 (FR-4, 0.9 mm thick) serving as a base is
The lower layer wiring 1 is formed by etching the copper foil that has been bonded in advance.
2 (signal wiring layer) is formed. (2) As shown in FIG. 3B, a photosensitive epoxy resin (Nippon Ciba Geigy: PR52) is applied over the entire surface of the lower wiring 12 by a bar coating method, and dried at 80 ° C. for 30 minutes. An insulating resin layer 13 of 40 μm is formed. (3) As shown in FIG. 3C, using a photomask in which a portion to be a via hole is masked, and having an exposure machine using a super-high pressure mercury lamp as a light source, exposure energy of 3000
Exposure was performed at mJ / cm ² . Developer (Nippon Ciba Geigy:
DY90), developed at 90 ° C. for 30 minutes, then 1
Heat treatment was performed at 40 ° C. for 60 minutes to completely cure the resin, thereby forming via holes 14 having via hole diameters of 80 μm, 70 μm, and 60 μm. Here, via hole 14
Is formed with an overhang portion 13a. (4) As shown in FIG. 3 (d), the jet scrub (water + powder) conditions shown in Table 1 were applied to the prepared substrate by a jet 16 (water flow containing an abrasive) from a nozzle 15. Removes the overhang portion 13a.
As a result, abrasive count # 220, slurry concentration 20%,
When the pressure is 5 kg / cm ² , the nozzle distance is 45 mm, and the spraying time is 240 seconds, the overhang portion 13a of the substrate
Can be completely removed. (5) A current film 17 is formed on the substrate by electroless copper plating, as shown in FIG. (6) Next, as shown in FIG. 3F, a plating resist 18 is formed with a positive type liquid resist, and a pattern copper plating 19 is applied. (7) Next, as shown in FIG. 3G, the plating resist 18 is peeled off. (8) Next, as shown in FIG. 3 (h), the upper wiring 20 is obtained by selectively removing only the current film 17 other than the pattern copper plating 19.

FIGS. 4A to 4I are process sectional views showing a third conventional example (for example, Japanese Patent Laid-Open No. 09-298362).
Reference).

First, as shown in FIG. 4A, a copper clad laminate (copper clad l) having a copper foil film adhered to both surfaces is provided.
A printed circuit pattern 112 is formed on the substrate 110 by a usual photolithography method. At this time, FIG.
As described above, when the pattern 112 is subjected to the blackening reduction process, the adhesion of the photosensitive insulating resin applied on the pattern can be further improved. Thereafter, as shown in FIGS. 4C to 4H, a photosensitive insulating resin 114 and a photosensitive insulating resin 116 are applied on the substrate on which the blackening film 113 is formed, and a photo via hole 120 is formed. The conductive circuit layer 130 is further formed on the layer, and it is preferable that the resin layer is applied first and second to a thickness of about 17 to 115 μm. If the insulating resin layer 114, the insulating resin layer 1
When the thickness of the layer 16 is less than 17 μm, not only the insulation may be reduced and signal interference may occur, but also the bending of the underlying circuit pattern may be exposed as it is and the surface shape may be changed due to the unevenness of the product surface. There's a problem. On the other hand, if the thickness of the insulating resin layer exceeds 115 μm,
The plating inside 20 is difficult and undercut (underc)
ut), the contact reliability of Cu plating is not only reduced, but there is no advantage in applying to a thin plate.

The coating step of the present invention for forming such a resin insulating layer will be described in detail. First, as shown in FIG. 4C, a photosensitive layer is formed on the substrate 110 on which the blackening film 113 is formed. The insulating resin 114 is first applied to an appropriate thickness using a printing plate, so that one side is printed and then semi-cured by a pre-drying step, and then the other side (not shown) is formed in the same manner. A photosensitive insulating resin is applied, pre-dried and semi-cured. As described above, when the primary photosensitive insulating resin 114 is applied, a positive type mask film (positive mask film) having an unexposed portion is vacuum-deposited on a pattern portion to be electrically connected to the inner layer so as not to be exposed. And expose. Thereafter, the unexposed portion on the photosensitive insulating resin is developed to form a V-shaped photo via hole as shown in FIG. After that, as shown in FIG. 4D, one of the primary photosensitive insulating resins 114 in which the photo-via holes 122 are formed is applied on one side of the primary photosensitive insulating resin.
After applying the secondary photosensitive insulating resin by the same method as the next coating method, pre-drying and temporarily curing, apply the secondary photosensitive insulating resin on the other primary photosensitive insulating resin by the same method, It is dried, temporarily cured, and exposed. At this time, the formation of the via hole 124 by the secondary exposure is made larger than the via hole of the primary resin layer, and as shown in FIG.
14. The final photo via hole 120 formed in the resin layer 116 maintains the V-shape.

The diameter of the via hole 124 formed by the second exposure and development is made about 1.05 times or more larger than the diameter of the via hole 122 formed by the first exposure and development.
Preferably, it is about 1.05 to 20 times.

The thickness ratio of the primary and secondary photosensitive insulating resins is 1
Secondary photosensitive insulating resin thickness: Secondary photosensitive insulating resin thickness = 10
~ 81: 19 ~ 90 is desirable. When the thickness of the primary photosensitive insulating resin is smaller than 10:90 with respect to the thickness of the secondary photosensitive insulating resin, the thickness of the secondary photosensitive insulating resin is too large, and Due to the difficulty, a target V-shaped via hole is formed with a via hole that is greatly undercut, so that the plating reliability on the bottom surface of the via hole is reduced during plating for interlayer conduction.

On the other hand, when the thickness of the primary photosensitive insulating resin is 81:19 or more with respect to the thickness of the secondary photosensitive insulating resin, the thickness of the secondary photosensitive insulating resin is too small. As the thickness on the Cu conductor circuit becomes thinner, the applied thickness of the photosensitive insulating resin required for the role of the intermediate insulating layer becomes thinner, resulting in insufficient interlayer insulation and lowering the insulation reliability of the product. .

The predrying performed after the application of the primary and secondary photosensitive insulating resins is performed at a temperature in the range of 5 to 130 ° C. for 5 to 45 minutes. When the drying temperature is less than 50 ° C. or the drying time is less than 5 minutes, a solvent [butyl carbinol (but) in the photosensitive insulating resin is used.
An insulating resin such as yl carbinol or butyl cellosolve is located on the surface of the coating film and is exposed to ultraviolet light (ultra-violet).
(Hereinafter, abbreviated as “UV”.) The light transmission is hindered, resulting in development with insufficient exposure, making it difficult to form a photo-via hole. Surface morphology transfer and stickiness occur.

When the drying temperature exceeds 130 ° C. or when the drying time exceeds 45 minutes, reactive radicals in the photosensitive insulating resin are generated.
Due to the overreaction, it is difficult to develop at the time of development even after irradiation with an appropriate exposure amount, so that formation of a photo via hole becomes difficult.

The exposure amount at the time of exposure is 50 to 700 mj / c.
m^Two Is desirable because the exposure amount is 50 mj / c
m^Two If less than the appropriate reaction light of the photosensitive insulating resin
It is difficult to form photo-via holes due to insufficient volume.
The exposure amount is 700 mj / cm ^Two If it goes beyond
Even after development due to the scattering of light amount to the
Photo via hole is reduced,
This is because it becomes difficult to form a via hole.

If the developing time is less than 20 seconds, the unexposed portion on the photosensitive insulating resin is not completely developed.
Interlayer insulation due to the transfer of the photosensitive insulating resin occurs during Cu plating, and if the time is 130 seconds or more, the undercut on the bottom of the via hole in the unexposed portion on the photosensitive insulating resin becomes large, causing interlayer conduction. In this case, the reliability of plating on the bottom surface of the hole is reduced during the Cu plating.

Thereafter, as shown in FIG. 4 (f), a through hole 140 for interlayer conduction is formed by a usual method, and as shown in FIG. 1 (g), a substrate provided with a V-shaped via hole 120 is formed. The surface of the insulating layer is electroless Cu-plated by an ordinary method, and then immediately electrolytically Cu-plated to give the circuit plating layer 13
When 0 is provided, plating adhesion is excellent even inside the via hole 120, and interlayer adhesion is ensured. Further, when the plating layer 130 is formed, a pattern 131 is formed by a normal photo-engraving method and one-time electrolytic Cu plating, and finally, a solder resist is applied.
A desired build-up MLB can be obtained, and the obtained build-up MLB can have a diameter of about 50 to 400 μm.

[0017]

Conventionally, via holes in a multilayer wiring board in which wiring layers and insulating layers are alternately and repeatedly laminated on a base substrate are formed by forming via holes on an insulating material having a photosensitive group (positive type). In this method, light of a certain wavelength is applied only to the part to be exposed (exposure), and the part irradiated with light is removed with a solution (development). There has been a problem that the aspect ratio becomes severe and it becomes difficult to remove the insulating material in a uniformly selected portion.

In particular, in the third prior art, FIG.
After a via hole (122) is formed in the photosensitive insulating resin (114) in FIG. 4 (d), a via hole (122) is further formed on the via hole (122).
In (e), the photosensitive insulating resin (116) is applied to form the via hole (124).
Since the photosensitive insulating resin (116) enters the inside of the via hole (122) previously formed in FIG. 4 (c), the photosensitive insulating resin (114) and the photosensitive insulating resin (116) are eventually formed. ) Needs to be removed, and the effect of the aspect ratio is impaired, so it is difficult to reduce the diameter of the via hole.

[0019]

According to a first aspect of the invention, there is provided a via hole forming method, comprising: (a) a step of forming a photosensitive insulating material (507) on a base substrate (502) and a land (506); A first mask (508) having large holes 521a is placed on the photosensitive insulating material (507),
And (c) forming a large hole (521b) on the photosensitive insulating material (507) by performing a first development with a first light (510) having a light intensity of And (d) large holes (521) in the photosensitive insulating material (507).
b) a second mask (5) having small holes (522a) above
09) and the second light (51) having the second light intensity
1) performing a second exposure, and (e) performing a second development to perform a second development between the large hole (521b) having a diameter (d1) of the photosensitive insulating material (507) and the land (506). d
The via hole (520) is formed by forming the small hole (522b) of 2).
And a step of obtaining

The method for forming a via hole according to a second aspect of the present invention comprises the steps of:
In the invention, the first exposure amount is controlled to such an extent that the photosensitive insulating material (507) is not removed by more than a half in thickness in the next developing step.

The method of forming a via hole according to a third aspect of the present invention comprises the steps of:
In the invention of the first aspect, the diameter of the first mask (508) (d
1) is limited to the size of the land (506).

According to a fourth aspect of the invention, there is provided a via hole forming method comprising:
In the invention, the second exposure amount is set to a value such that the photosensitive insulating material (507) is removed to the land (506) in the next development step.

The method for forming a via hole according to a fifth aspect of the present invention comprises the steps of:
In the invention, the diameter (d) of the second mask (509)
2) is smaller than the size of the land (506).

In the via hole forming method of the sixth invention, first, a small hole is made to penetrate into the photosensitive insulating material (507), and then a large hole (521b) is formed. And a via hole forming method.

[0025]

Next, embodiments of the present invention will be described in detail with reference to the drawings.

FIGS. 1A to 1E are process sectional views showing an embodiment of the present invention. The multilayer wiring board is formed by alternately stacking wiring layers and insulating layers on a base substrate 502, and via holes are formed on lands 506 of the wiring layer.

FIG. 1A A photosensitive insulating material 507 is formed on the base substrate 502 and the lands 506.

FIG. 1B: A first mask 508 having a large hole 521a is placed on the photosensitive insulating material 507,
The first exposure is performed by the first light 510 having the light intensity of.

FIG. 1C: First development is performed to form a large hole 521b on the photosensitive insulating material 507.

FIG. 1D: Second mask 50 having small holes 522a on large holes 521b of photosensitive insulating material 507.
9 is placed, and the second exposure is performed by the second light 511 having the second light intensity.

FIG. 1 (e) A second development is performed to form a small hole 522 b having a diameter d 2 between the large hole 521 b having a diameter d 1 of the photosensitive insulating material 507 and the land 506, and forming a via hole 52.
Get 0.

The first exposure dose is controlled to such an extent that the photosensitive insulating material 507 is not removed by more than a half in thickness in the next developing step.

The diameter d1 of the first mask 508 is equal to the land 5
06 is the upper limit.

The second exposure amount is set so that the photosensitive insulating material 507 is removed to the land 506 in the next development step.

The diameter d2 of the second mask 509 is equal to the land 5
06 size.

The small holes may be first penetrated into the photosensitive insulating material 507, and then the large holes 521b may be formed.

[0037]

As described above, the method of forming a via hole according to the present invention reduces the thickness of the insulating material around the via hole in advance, and forms a via hole portion having a desired diameter in this thin portion. The aspect ratio of the thickness of the insulating material and the size of the via hole is relaxed, and there is an effect that a uniform via hole can be easily formed.

[Brief description of the drawings]

FIGS. 1A to 1E are process cross-sectional views showing an embodiment of the present invention.

FIGS. 2A and 2B are process cross-sectional views showing a first conventional example.

3 (a) to 3 (h) are process sectional views showing a second conventional example.

FIGS. 4A to 4I are process cross-sectional views showing a third conventional example.

[Explanation of symbols]

 502 Base substrate 506 Land 508 Mask 509 Mask 510 Light 511 Light 521a Large hole 521b Large hole 522a Small hole 522b Small hole

Claims (6)

[Claims] (A) forming a photosensitive insulating material (507) on a base substrate (502) and a land (506); and (b) forming a large hole 521a on the photosensitive insulating material (507).
Placing a first mask (508) having a first light intensity and a first light (510) having a first light intensity; and (c) performing a first development to form a photosensitive insulating material ( (D) forming a large hole (521b) on the 507); and (d) forming a large hole (521b) in the photosensitive insulating material (507).
Mask (50) having a small hole (522a)
9) placing a second light (511) having a second light intensity
And (e) performing a second development to perform a second development and to form a diameter (d2) between the large hole (521b) having a diameter (d1) of the photosensitive insulating material (507) and the land (506). Forming a small hole (522b) to obtain a via hole (520). 2. The via hole forming method according to claim 1, wherein the first exposure amount is suppressed to such an extent that the photosensitive insulating material is not removed by more than a half in thickness in a subsequent developing step. 3. The diameter (d1) of the first mask (508).
The via hole forming method according to claim 1, wherein the size of the via hole is limited to the size of the land (506). 4. The via hole forming method according to claim 1, wherein the second exposure amount has a value such that the photosensitive insulating material (507) is removed to the land (506) in the next developing step. 5. The diameter (d2) of the second mask (509).
2. The method according to claim 1, wherein the size of the via hole is smaller than the size of the land. 6. A method for forming a via hole, comprising: first, penetrating a small hole in a photosensitive insulating material (507), and then forming a large hole (521b).